Anybody ever calculated this out for a straight axle on a hot rod? Either with a transverse leaf spring or a quarter elliptical setup. I was just readin up on this subject and there isn't anything out there that shows how to measure it for the old stuff, just double a-arm setups and parallel leafs. Anybody done any of this or know how? Thanks
Seems like it would be kind of difficult. I think the amount the axle is dropped would be the determining factor. With the circle track cars I used to change front springs (coil) and use bigger ball joints and taller spindles. I also know relocating the pivot points of the A arms and using different length A arms gave me a more favorable RC. With a straight axle everything is pretty much fixed and symetrical. I would think the amount of drop an the axle and the arch of the spring would be the only way to change that. Of course I've never thought about it before and I'm probably 100% wrong.
Dropped or not the r/c will still be the center of the axle. This also applies to the rear axle also. However, changing the lateral locating linkage mounting points will change the r/c height.
With a solid axle,if you are not running a Panhard bar,Watt's Link,Jacobs ladder,etc. the roll center height is dictated by were the leaf spring(s) attatches.
In a car that uses a transverse leaf to both suspend and locate the axle, the roll center is found by projecting a line between the spring eyes. Where this line crosses the CL of the ch***is is the roll center. Where the lateral locating is done via a panard bar, the roll center is found where the CL of the panard bar crosses the CL of the ch***is. When using a Watts Linkage for lateral location, the roll center is located at the center of the bellcrank, which will/should always be on the CL of the ch***is. A jacobs ladder makes things more complex, because more than one bar is used in this linkage, we have to project an instant center to find the roll center. It's too hard to explain with text, so I drew up a pictar to illustrate: Hope that helps.
There has been much written on this in tech sources but here goes my 2 bits worth, Like Kazootie said, the roll center on straight axles front or rear is determined from where the lateral location device is placed, Solid rear axle cars (live axle) like most hot rods need a fairly high roll center because remember the roll couple is the difference between the center of gravity and the height of the roll center. (leverage) if the roll center was too high the car would lean into the corner! no kidding, the trick part is the have the front and rear close to the same, the tough part is getting the front roll center high enough (radiator and stuff in the way) on cars with large engines sticking everywhere...think blown big block early roadster. Done correctly a sway bar is not needed. also the trick is to get the rear roll center height (with panhard bar or ?) high enough without sacrificing the floor! Also there is not much room for a long enough bar to work well. next.
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